Abstract: Soda residue, fly ash and sodium silicate solution have been synthesized as a new grouting material for filling goafs. In the present research, the solidification mechanism is explored by methods of scanning electron microscope and mutual blending. Moreover, the impacts of mix ratio, sieving particle size of soda residue, and curing condition on engineering indicators (compressive strength, setting time, and stone rate, among others) are examined by tests. Results demonstrate that the early solidification of slurry is determined by the calcium silicate hydrate gel (C-S-H) generated by calcium components of soda residue reacting with sodium silicate solution; and the later strength increment is determined by aluminosilicate polymer gel (N-A-S-H) formed by alkali-activated class F fly ash. The mix ratio of raw materials significantly affects the engineering properties of the slurry. With the shrinkage of sieving particle size of soda residue, the fluidity, setting time, and stone rate decrease, whereas compressive strength increases. Particle size 0.5 mm is the threshold for the increment of strength cured for 28 days. High temperature and humidity is favorable for the solidification process of slurry.

Key words: grouting material, goaf, solidification mechanism, sieving particle size of soda residue, engineering properties, influential factors